בדיקת חמץ וביעור יצר הרע - פסחים פרק א משנה א

On the evening of the fourteenth [of Nissan] they search they house for chametz by the light of a lamp. Every place into which chametz is not brought does not require searching, So why did they rule: two rows of the wine cellar [must be searched]? [This is actually] a place into which chametz might be taken. Bet Shammai say: two rows over the front of the whole cellar; But Bet Hillel say: the two outer rows, which are the uppermost.

On the evening of the fourteenth, we check for chamets by candlelight, not by sunlight, not by moonlight, but rather only by candlelight (since the candlelight is greater). Even though there's no explicit proof for this, it's a remembrance for that which is discussed (Tzefaniah 1) "And in that time I will look through Jerusalem by candle" and that which it says (Proverbs 20) "The candle of God is a human soul". Bet Shamai say: "Two rows on the entire cellar -- the outer row which faces the door, and the uppermost which faces the ceiling. [but the lower rows and the inner rows don't need checking]." Bet Hillel say: "[The outer row is] the uppermost which faces the door and those under it. However the rows that are more inwards from it don't need checking".

The mishna states that one searches for leaven by the light of the lamp, etc. The Gemara asks: From where are these matters, i.e., that the search should be conducted by the light of the lamp, derived? Rav Ḥisda said: We derive it by the hermeneutic principles of verbal analogy and juxtaposition: The term finding in one context is derived from finding in another context, and finding is derived from the word searching, and this searching is derived from searching elsewhere, and searching there is derived from the word lamps, and lamps is derived from lamp. The Gemara cites the relevant verses included in the above derivation. Finding in one context is derived from finding in another context by verbal analogy, as it is written here: “Seven days leaven shall not be found in your houses” (Exodus 12:19), and it is written there: “And he searched, starting with the eldest, and ending with the youngest; and the goblet was found in Benjamin’s sack” (Genesis 44:12). And the word finding in this verse is connected to searching in that same verse by juxtaposition, as the verse says: “And he searched... and was found.” And searching is derived from lamps by means of juxtaposition, as it is written: “And it shall come to pass that at that time I will search Jerusalem with lamps” (Zephaniah 1:12). And finally, the word lamps is derived from lamp by means of juxtaposition, as it is written: “The spirit of man is the lamp of God, searching all the inward parts” (Proverbs 20:27). Together these verses indicate that the search for leaven must be conducted by the light of the lamp.